The present invention relates to a process for preparing o-chloromethylbenzoyl chlorides of the formula I, 
in which R1 to R4 are as defined above, with gaseous or different and are hudrogen, C1-C4-alkyl, halogen or trifluoromethyl, by reacting benzo-fused lactones of the formula II 
in which R1to R4are as defined above, with gaseous or liquid phosgene,its dimers or trimers. liquid phosgene, its dimers or trimers.
o-chloromethyl-substituted benzoyl chlorides are important intermediates for preparing, for example, pesticidally active compounds as described in the patents EP-A 460 575, EP-A 463 488, WO-A 95/18789, WO-A 95/21154 and WO-A 97/15552.
o-Chloromethyl-substituted benzoyl chlorides can be prepared, for example, by reacting benzo-fused lactones with thionyl chloride or phosgene.
EP-A 676 389 describes the preparation of o-chloromethylbenzoyl chlorides from benzo-fused lactones using thionyl chloride in the presence of a catalyst. To achieve complete conversion, reaction temperatures of 160-170xc2x0 C. are required, at which thionyl chloride is already partially decomposed, resulting in the formation of troublesome byproducts.
In WO-A 99/16743, the reaction with thionyl chloride is carried out in the presence of a quaternary ammonium salt and a Lewis acid at 90-100xc2x0 C. However, quaternary ammonium salts are problematic from an environmental point of view and have the following technical disadvantages: owing to sublimation, parts of the plants may become blocked. Furthermore, the salts are hygroscopic, which may lead to water being introduced and to a higher consumption of chlorinating agent. Finally, the ammonium salts interfere with the distillative purification of the o-chloromethylbenzoyl chlorides.
Carrying out the reaction using thionyl chloride as chlorinating agent is disadvantageous since sulfur dioxide, which has to be worked-up or neutralized, is formed as coproduct in the synthesis. If the chlorinating agent used is phosgene, carbon dioxide, which does not have to be disposed of, is the only byproduct.
EP-A 583 589 describes a process for preparing o-chloromethylbenzoyl chlorides by phosgenation of benzo-fused lactones in the presence of a catalyst at 170-180xc2x0 C. In contrast to thionyl chloride, phosgene is thermally stable under these conditions; however, the handling of phosgene and its hold up in the condenser at the high temperatures involved is made more difficult by increased safety precautions. Furthermore, under these conditions, the reaction product is under high thermal stress, which may result in its partial decomposition.
In WO 97/12854, triarylphosphine oxides are used as special catalyst type for the reaction, owing to which the use of hydrogen chloride can be dispensed with; however, this does not result in an improvement in the required reaction conditions with respect to the objectionably high reaction temperatures and the resulting safety precautions required.
It is an object of the present invention to provide an economical process, capable of being carried out on an industrial scale, for preparing o-chloromethylbenzoyl chlorides which does not have the abovementioned disadvantages and still affords high yields.
We have found that this object is achieved by the process mentioned at the outset, which comprises carrying out the reaction with phosgene, its dimers or trimers in the presence of catalytic amounts of a Lewis acid and catalytic amounts of a phosgenation catalyst.
The starting materials used are benzo-fused lactones (phthalides) of the formula II, 
in which R1 to R4 can be identical or different and are hydrogen (H), C1-C4-alkyl, halogen (fluorine, chlorine, bromine or iodine) or trifluoromethyl. Preference is given to using unsubstituted phthalide.
The chlorinating agent used is preferably gaseous or liquid phosgene. Furthermore, it is also possible to use dimers (trichloromethyl chloroformate, xe2x80x9cdiphosgenexe2x80x9d) or trimers of phosgene (bistrichloromethyl carbonate, xe2x80x9ctriphosgenexe2x80x9d) or mixtures of these chlorinating agents.
Suitable phosgenation catalysts are, in particular, nitrogen compounds and phosphorus compounds. Examples which can be considered are N,N-disubstituted formamides, hexaalkylguanidinium salts, trialkylphosphines or triarylphosphines which may be substituted or unsubstituted in the aryl moiety, trialkylphosphine oxides or triarylphosphine oxides which may be substituted or unsubstituted in the aryl moiety, N-substituted imidazoles and substituted or unsubstitited pyridines. Particular preference is given to the pyridines of the formula IIIa, 
where R is hydrogen or methyl, and to phosphine oxides of the formula IIIb, 
in which R1 to Rxe2x80x2xe2x80x3 can be identical or different and are C1-C10-alkyl or unsubstituted or C1-C4-alkyl-substituted phenyl and the index n is 0 or 1. Particular preference is given to 3-methylpyridine (xcex2-picoline) and unsubstituted triphenylphosphine oxide.
The use of liquid trialkylphosphine oxides has, in particular, technical advantages (no need to handle solids, easier discharge of the distillation residue during purification). The tri-C6-C8-alkylphosphine oxides available under the trade name Cyanex(copyright) (for example. Cyanex(copyright) 923 from Cyanamide) are, for example, suitable here. Liquid trialkylphosphine oxides combined with Lewis acids, such as tri(C1-C4-alkyl) borates and boric acid, have been found to be particularly useful.
The phosgenation catalyst is generally added in amounts of from 0.1 to 20 mol %, based on the amount of benzo-fused lactone used, and is preferably added in amounts of from 1 to 10 mol %.
Suitable Lewis acids are, in particular, boron compounds, such as, in particular, BF3, BCl3 or complexes thereof with oxygen compounds, sulfur compounds or nitrogen compounds, tri(C1-C4-alkyl) borates and boric acid (H3BO3) itself. Furthermore suitable are AlCl3, alkylaluminum dichlorides and dialkylaluminum chlorides, and heterogeneous Lewis-acidic alumosilicates of the zeolite type. Particular preference is given to BF3, BCl3 and complexes thereof with ether (in particular diethyl ether), water (dihydrate), alcohol (in particular methanol), sulfide (in particular dimethyl sulfide) and amine (in particular ethylamine). Particularly suitable are, for example, BF3 etherate and BF3 dihydrate.
The Lewis acid used is particularly preferably boric acid or tri(C1-C4-alkyl) borate. Such processes give excellent yields and have the advantage that the reaction mixtures are free from fluoride ions. Compared to the analogous reaction where the Lewis acid used is BF3, the entire apparatus can be simplified.
The Lewis acid is added in amounts of from 0.1 to 20 mol %, based on the amount of benzo-fused lactone used, preferably in amounts of from 0.5 to 5 mol %.
In a further preferred embodiment of the process, the catalyst used is a complex, formed beforehand, of Lewis acid and the phosgenation catalyst. In general, this complex is employed in a concentration of from 0.1 to 20 mol %, based on the amount of benzo-fused lactone used. The catalyst used is preferably a complex of BF3 and a methyl-substituted pyridine, and particular preference is given to the BF3-xcex2-picoline complex.
If desired, hydrogen chloride can be introduced in parallel to the introduction of phosgene, to accelerate ring-opening. However, the introduction of hydrogen chloride during the synthesis is preferably dispensed with.
Furthermore, it may be advantageous to employ heterogeneous Lewis-acidic catalysts, such as, for example, zeolites of the faujasite type in which some or all of the exchangeable cations have been replaced by protons. A heterogeneously catalyzed reaction has the advantage that it can be carried out in a fixed bed. The heterogeneous catalyst is employed in amounts of from 0.01 to 10% by weight and preferably in amounts of from 0.1 to 1% by weight, based on the amount of benzo-fused lactone used.
The reaction temperature is generally 110-200xc2x0 C. and preferably 130-160xc2x0 C.
The process is preferably carried out in the absence of a solvent. However, it is possible to add a solvent which is inert to phosgene. Inert solvents are, for example, aromatic hydrocarbons, such as toluene, o-, m- or p-xylene or mixtures thereof, chlorinated aromatic hydrocarbons, such as chlorobenzene or dichlorobenzenes, or cyclic carbonates, such as ethylene carbonate or propylene carbonate.
The process can be carried out either continuously or batchwise.